In recent years, there has been a growing demand for optical information recording/reproducing devices capable of recording/reproducing information on/from two or more of different kinds of optical information recording media based on different standards, such as CD (Compact Disc), DVD (Digital Versatile Disc), EVD (Enhanced Versatile Disc), BD (Blu-ray Disc) and HD-DVD (High Definition Digital Versatile Disc).
In general, different kinds of optical information recording media are different in specification, such as the wavelength of light used and the thickness of a cover layer of the optical information recording medium (a distance from its surface to the information recording surface of the medium). Therefore, if an objective lens specifically engineered for a certain kind of optical information recording medium is used for a different kind of optical information recording medium, significant aberration (i.e., spherical aberration and the like) occurs. As a result, information cannot be suitably recorded and reproduced on and from the optical information recording medium.
For example, in order to properly record/reproduce information on/from every kind of optical information recording media based on different standards, an optical pickup may be provided with multiple kinds of objective lenses engineered for the different optical information recording media, respectively. In this optical pickup including the different kinds of objective lenses, it is necessary to select one from the objective lenses in response to the kind of the target optical information recording medium on or from which information is recorded or reproduced, and therefore a system for selecting the objective lens is required. As a result, the structure of the optical pickup is complicated, resulting in increase in size and cost of the optical pickup.
In connection to such a problem, various methods have been proposed to correct or reduce the aberration (i.e., spherical aberration and the like) which occurs in recording/reproducing information on/from various kinds of optical information recording media based on different standards with use of a single objective lens.
For example, Patent Publication 1 discloses a technique of using a polarized phase correction element including a polymer liquid crystal layer for correcting the spherical aberration (Patent Publication 1: Japanese Unexamined Patent Publication No. 2003-149443).
However, even according to the technique disclosed by Patent Publication 1, it is still difficult for the conventional optical pickup to record/reproduce information on/from various kinds of optical information recording media based on different standards in a suitable manner.
Under these circumstances, the present invention has been achieved. An object of the present invention is to provide an optical pickup capable of suitably recording/reproducing information on/from each of the various kinds of optical information recording media based on different standards.